In relation to the events surrounding the tsunami at Fukushima and the ensuing loss of coolant accident, interest in developing more accident-tolerant fuels has greatly increased. Despite the success of oxide fuels, their thermal conductivity is a major drawback in normal operation, transients, accident scenarios, and storage. An innovative fuel design is herein described that lowers the peak temperature of the fuel by approximately 640 degrees Celsius at peak power. Initial modeling results are summarized and compared to the case of conventional UO2 pellet fuel. Performance requirements have been identified for candidate materials to be incorporated into the design; a significant manufacturing infrastructure exists for some of these candidates.
Prior efforts to improve the thermal conductivity of UO2 fuels include investigation of dispersion fuels such as cercers and cermets. Economic hindrances to such fuel forms include the loss of reactivity due to the reduced U-235 density and increased manufacturing costs. Dispersion fuels characteristically include a large amount of inert material and volume, so that the U-235 enrichment would have to be substantially increased above 5% to account for the displaced volume of UO2.
Annular fuels provide an alternative way to reduce peak fuel temperature. The peak temperature of the fuel is lowered due to the reduction in the conduction path length. This design has been applied to fast reactor oxide fuels that operate at high linear powers to guard against fuel melting. In the case of light water reactor fuels, the U-235 enrichment would again have to be increased, but not to the extent needed with dispersion fuels.